How are miraj's formed?

Answer 1

Mirage is an optical illusion which occurs usually in deserts on hot summer days. The object such as the tree appears to be inverted as if the tree is on the bank of a pond of water. consider the figure below:

On a hot summer day, temperature of air near the surface of earth is maximum. The upper layers of air have gradually decreasing temperature. Therefore, density and refractive index of air goes on increasing slightly with height above the surface of earth.

A ray of light from the top of a tree goes from denser to rarer medium bending away from the normal. At a particular layer, when the angle of incidence becomes greater than the critical angle, total internal reflection occurs and the totally reflected ray reaches the observer. As a result the observer sees the inverted mirror image of the tree .